1. Field of the Invention
The present invention relates to a laminate, a preparatory support for producing the laminate, a method for producing a laminate, and a method for producing a device.
2. Background Art
In the field of semiconductor technology, studies are being made to produce a thinner semiconductor wafer (hereinafter also referred to simply as “wafer”) in order to respond to the progress toward thinner packages and higher-density devices through development of chip stacking techniques. Thinning of a wafer is performed by so-called back grinding, i.e. grinding of a wafer surface opposite to a patterned surface. Due to warpage of a wafer caused by thinning, however, such wafer thinning entails problems such as difficulty in securing the uniformity of thickness upon grinding of the wafer, difficulty in transporting the wafer, the occurrence of chipping (edge chipping) during dicing of the wafer into chips, etc. To carry out wafer back grinding with high thickness uniformity, facilitate wafer transport and prevent the occurrence of chipping, a technique has been employed which involves fixing a wafer before thinning on a rigid support, performing back grinding, transport and dicing of the fixed wafer, and detaching the wafer or diced chips after thinning from the support.
With a view to providing a laminate in which a substrate to be ground is fixed on a support, and the substrate after grinding can be easily detached from the support, patent document 1 describes a laminate comprising a substrate to be ground, a bonding layer in contact with the substrate, a photothermal conversion layer containing a light absorbing agent and a heat decomposable resin, and a light-permeable support. The photothermal conversion layer decomposes when the layer is irradiated with a radiation energy after grinding the substrate surface opposite to the surface in contact with the bonding layer, so that the substrate after grinding can be separated from the light-permeable support.
With a view to providing a method which, in a process for producing semiconductor chips comprising the step of dicing a semiconductor wafer, can effectively prevent chipping during the dicing step, patent document 2 describes a method for producing semiconductor chips. In particular, the chip production method comprises the steps of: applying a photothermal conversion layer containing a light absorbing agent and a heat decomposable resin onto a light-permeable support (the photothermal conversion layer, when irradiated with a radiation energy, converts the radiation energy into heat and is decomposed by the heat); providing a semiconductor wafer having a patterned surface with a circuit pattern, and a non-patterned surface opposite to the patterned surface, bonding the semiconductor wafer and the light-permeable support together with a photo-curable adhesive such that the patterned surface faces the photothermal conversion layer, and applying light to the photo-curable adhesive layer from the light-permeable support side to cure the photo-curable adhesive layer, thereby forming a laminate having outermost the non-patterned surface; grinding the non-patterned surface of the semiconductor wafer until a predetermined thickness of the semiconductor wafer is reached; dicing the ground semiconductor wafer from the non-pattered surface side into semiconductor chips; applying a radiation energy to the photothermal conversion layer from the light-permeable support side to decompose the photothermal conversion layer, thereby separating the semiconductor chips having the adhesive layer from the light-permeable support; and removing the adhesive layer from the semiconductor chips.
In the field of liquid crystal display (LCD) technology using a thin film transistor (TFT), an LCD is produced through the step of forming a thin transistor on a transparent substrate e.g. by CVD. Because high heat resistance is required for the transparent substrate, quartz glass or heat-resistance glass is used for the substrate. Such a substrate of quartz glass or heat-resistance glass is fragile and heavy in weight, and therefore entails the problem of difficult handling upon the production of a large-sized LCD. Therefore, a method is employed in which after a thin transistor is formed on a rigid support, a quartz glass or high-resistant glass substrate is superimposed as a transfer medium on the support, and then the support is detached.
With a view to providing a detachment method capable of easy detachment of an object irrespective of the properties, conditions, etc. of the object, and in particular capable of transfer to various transfer media, patent document 3 describes a detachment method for detaching an object, which is present on a substrate via a separation layer which is a laminate of a plurality of layers, from the substrate, the method comprising irradiating the separation layer with light to cause separation of the layer within the layer and/or at the interfaces, thereby detaching the object from the substrate.    Patent document 1: Japanese Patent Laid-Open Publication No. 2004-64040 (claim 1, paragraph 0005)    Patent document 2: Japanese Patent Laid-Open Publication No. 2005-159155 (claim 1, paragraph 0007)    Patent document 3: Japanese Patent Laid-Open Publication No. H10-125929 (claim 1, paragraph 0006)
Thus, in the fields of semiconductor technology and LCD technology, in order to overcome the problems such as deflection or warpage of a wafer upon the production of the wafer or a thin transistor, difficulty in processing or handling of a wafer, on which a thin transistor is to be formed, because of the fragileness of the substrate, etc., a technique is used which involves producing a wafer or a thin transistor with the wafer fixed on a rigid support, and then detaching the rigid support.
Problems similar to the wafer deflection or warpage problem and the problem of difficulty in processing or handling a substrate because of its fragileness, will occur when producing a thin device comprising a flexible substrate and a device formed on it, such as an organic electroluminescence device (organic EL device), an organic transistor device or a solar cell device. In particular, a large-sized flexible substrate is likely to bend or break depending on the material used. It is difficult to transport such a large-sized substrate in a horizontal position or in a stable manner, making it difficult to form a device on the flexible substrate.
To enable stable production of such a thin device, therefore, application of the above-described techniques employed in the fields of semiconductor wafers and LCDs has been an important technical problem. In particular, in such an applied technique, a flexible substrate is fixed on a rigid support via an adhesive layer and a photothermal conversion layer which can be detached by irradiation with laser light. After forming a device on the flexible substrate fixed on the support, the photothermal conversion layer is irradiated e.g. with laser light, thereby decomposing the photothermal conversion layer and separating the rigid support from the substrate.